Vapor lamp standby apparatus

ABSTRACT

A new and improved apparatus for providing light when a vapor lamp, such as a mercury vapor lamp, has been extinguished because of a temporary failure in the electrical power supply of such lamp.

United States Patent [191 Peterson et al. Jan. 1, 1974 [54] VAPOR LAMP STANDBY APPARATUS 3,699,382 10/1972 Franke 315/87 x J '7 [75] Inventors: John D. Peterson; Walter E. Bates, 3,6S9,l46 4ll97- Munson 315/9- both of Seabrook, Tex.

[73] Assignee: W. E. Bates Engineering Co., primary Examiner H. K Saalbachl Seabrook, Assistant Examiner-Richard A. Rcsenberger [22] Filed: June 5, 1972 Attorney-Pravel, Wilson & Matthews [21] Appl. No.: 259,553

[52] US. Cl. 315/91, 315/92, 315/171, 57 S C 315/176 [51] Int. CL. H05b 41/46, H05b 37/04, H05b 37/03 58 Field of Search 315/87, 88, 89,90, A new and Improved apparatus Provldmg 11gb 315/9], 92, 93 94 171, 173 176 when a vapor lamp, such as a mercury vapor lamp, has been extinguished because of a temporary failure in [56] References Cited the electrical power supply of such lamp.

UNITED STATES PATENTS 3,582,708 6/1971 Snyder 315/91 9 Claims, 7 Drawing Figures Pmemamm H I 3.733.332

SHEU 2 BF 2 f wu 1 VAPOR LAMP STANDBY APPARATUS BACKGROUND OF INVENTION 1. Field of the Invention The present invention relates to standby apparatus for vapor lamps.

2. Description of the Prior Art As is known, mercury vapor lamps were desirable for lighting large areas due to their efficiency and high light output. However, when electrical power to the mercury lamp was temporarily interrupted, the lamp would deenergize and have no light output. The lamp then had to be allowed to cool before re-ignition, due to the inhibition of starting by the hot mercury vapor in the lamp.

Several prior art attempts have been made to provide a standby light source while the mercury lamp was cooling before re-ignition. Certain apparatus, such as those disclosed in US. Pat. Nos. 3,599,036; 3,611,432; and 3,636,404 included circuitry responsive to the current flowing to the mercury lamp to energize and deenergize the standby lamp. Since the circuitry had to be able to carry the currents drawn by the mercury lamp,

such circuitry was expensive because of the high power requirements, and subject to a high degree of wear.

Other prior art apparatus, such as that of US. Pat. No. 3,517,254, used semiconductors having predeter mined voltage characteristics corresponding to the starting voltage and current and operating voltage and current characteristics of the lamp. Different semiconductors and circuits were required when additional mercury lamps were included in the apparatus, since the starting and operating characteristics changed when additional lamps were included.

SUMMARY OF THE INVENTION Briefly, the present invention provides a new and improved apparatus for energizing a standby lamp, when a'vapor lamp, such as a mercury lamp, is de-energized or extinguished in response to an interruption of electrical power being supplied to the vapor lamp. The apparatus maintains the standby lamp energized until the vapor lamp is re-ignited or energized. In the apparatus of the present invention, a sensing means connected in parallel with the vapor lamp senses the status of the vapor lamp, and a standby means provides light when the vapor lamp is de-energized.

The sensing means includes a control means responding to the extinguishing of the vapor lamp to control the standby means. A voltage divider means protects the control means by preventing the high voltage level present across an extinguished, hot lamp from being applied to the control means so that the control means need not operate under high power levels. A clamping means in the voltage sensing means causes the voltage present at the terminals of the extinguished lamp to be increased to a high level in order that re-ignition of the vapor lamp is facilitated.

The standby means includes a standby lamp means, a charge storage means for accumulating an electrical charge, a trigger means for energizing the standby lamp in response to a predetermined charge on the charge storage means, and a switch means responsive to the control means of the sensing means for preventing electrical charge from accumulating in the charge storage means when the vapor lamp is energized.

It is an object of the present invention to provide a new and improved vapor lamp standby apparatus.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic electrical circuit diagram of the present invention; and

FIGS. 2(A) through 2(F), inclusive, are illustrations of voltage waveform diagrams, as a function of time, present in the electrical circuit of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENT In the drawings, the letter A designates generally the apparatus of the present invention for providing standby illumination when a vapor or high intensity discharge lamp L, or a plurality of such lamps L, are deenergized in response to an interruption of electrical power. The interruption may be a temporary interruption, caused by a short-term transient lasting only a few milliseconds, or a long-term interruption of a few minutes or more. As is known in the art, the heated vapor in a vapor lamp inhibits re-ignition of the lamp after the lamp has become de-energized because of the increased ignition voltage required when the vapor is heated. Accordingly, the heated vapor must cool for a period of minutes so that the ignition voltage required to re-ignite the lamp L is within the power output requirements of the power supply of such lamp.

In the preferred embodiment of this invention, the vapor or high intensity discharge lamp L is a mercury vapor lamp. However, it should be understood that other vapor or high intensity discharge lamps, such as sodium or halide lamps, are equally suitable for use with the present invention.

Considering the apparatus A more in detail (FIG. 1), a control circuit K energizes a standby lamp S in re sponse to de-energization of the vapor lamp or lamps L. As will be more evident hereinbelow, the control circuit K maintains the standby lamp S energized until the illumination output of the lamps L reaches a predetermined intensity, as indicated by the voltage drop across such lamps.

Input conductors 11 and 12 are connected at terminals 11a and 12a, respectively, to a suitable source of alternating current power to energize the vapor lamps L. A current-limiting ballast transformer 14 is electrically connected by the conductors 11 and 12 to the input terminals 11a and 12a. The ballast transformer 14 is of the conventional type used with vapor or discharge lamps. A capacitor 14 is connected to the ballast transformer 14 at a first output 14a thereof. The capacitor 15 controls the degree of saturation of the ballast transformer 14 so that the current provided to the discharge lamps L does not exceed the desired operating level.

The vapor lamps L include a pair of mercury discharge lamps in the preferred embodiment electrically connected in series between a second output 14b of the ballast transformer 14 and the capacitor 15. As has been set forth hereinabove, it should be understood that other vapor lamps or high intensity discharge lamps may be used with the present invention. It should further be understood that, when desirable for illumination output purposes, more mercury discharge lamps than the two shown in theaccompanying drawings may be electrically connected in series between the terminal 14b and the capacitor 15. It should further be understood that a single vapor lamp L may be used with the apparatus A, if desired. As will be set forth hereinbelow, the control circuit K is readily adapted for use with different numbers of vapor lamps L without requiring extensive redesign and circuit changes to operate therewith.

Considering the control circuit K more in detail, a sensing circuit 20 is electrically connected at terminals 20a and 20b in a parallel circuit arrangement with the vapor lamps L between the capacitor and the terminal 14b of the ballast transformer T4. The voltage appearing at the input terminals 200 and 2tlb of the sensing circuit is substantially the same voltage as the voltage drop across the vapor lamps L due to the parallel electrical circuit connection between the lamps L and sensing circuit 20. The parallel electrical circuit connection between the sensing circuit 20 and the lamps L permits the sensing circuit 20 to sense the operating condition of the vapor lamps L as well as the illumination output of the lamps L, as will be more evident hereinbelow.

A control relay 22 senses the de-energization of the vapor lamps L and energizes the standby lamp S in response to such de-energization. A bypass or shunt capacitor 23 is connected in parallel with the control relay 22 in order to isolate the relay 22 from short term transient effects or the effect known in the art as chatter in contacts controlled by the relay 22.

A voltage divider network 25-protects the control relay 22 from the high voltages present across the terminals 20a and 20b of the sensing network 20. The voltage divider network 25 includes a first resistor 26 connected in series with the control relay 22. A second resistor 27 of the voltage divider network 25 is connected in parallel with the series connected first resistor 26 and the control relay 22.

The resistance of the resistor 26 is preferably of a magnitude substantially equal to the impedance of the control relay 22 so that the potential at a connection 26a between the resistor 26 and the relay 22 is substantially one-half of the potential drop across the series connected first resistor 26 and the control relay 22. in this manner, the control relay 22 is protected from high voltage levels present across the terminals 249a and 20b of the sensing network 20.

The resistance of the second resistor 27 is preferably substantially twice the magnitude of the resistance of the first resistor 26. In this manner, the second resistor 27 connected in parallel with the relay 22 and resistor 26 draws a substantially equal amount of current to the current flowing through the resistor 26 and relay 22. The resistor 27 thereby serves to further protect the control circuit 20 from high voltage levels present at the input terminal 20a and 20b of sensing network 2%. The resistor 27 further serves to provide a load in parallel with the control relay 22 and resistor 26 in order to offset the voltage appearing at the terminals 20a and 205 a desired amount when the vapor lamp L is deenergized.

The voltage drop resistor 28 of the voltage divider 25 is connnected in series with the resistor 26 and control relay 22, and is further connected in series with the second resistor 27. The voltage drop resistor 28 has a resistance value substantially equal to the resistance of the resistor 27 and the impedance of the series connected resistor 26 and relay 22. In this manner, the potential at a terminal 25a is reduced to substantially one-half of the potential at the input terminals 20a and 20b at the sensing network 20.

The resistance value of the resistor 28 may be varied in accordance with the number of vapor lamps L connected in parallel with the sensing network 20. When the number of vapor lamps L is increased, the resistance value of the voltage drop resistor 28 is increased in order to increase the voltage drop thereacross and maintain the potential at the terminal 25a at the desired level. When a single vapor lamp L is used, the voltage drop resistor 28 is reduced in value, and may be removed from the circuit.

A clamping diode 29 or other suitable unidirectionally conductive means is included in the sensing network 20. As will be set forth hereinbelow, the clamping diode 29 and the capacitor 15 coact and increase the voltage present at the terminals 20a and 20b across the vapor lamps L when such lamps are de-energized in order to facilitate re-ignition of the vapor lamps L.

A standby circuit 30 of the control circuit 20 energizes the standby lamp S when the vapor lamps L are de-energized. A pair of input conductors 31 and 32 electrically connect the standby circuit 30 to a suitable power supply. As indicated in the drawings, the conductors 3i and 32 electrically connect the standby circuit 30 to the conductors 11 and 12 and to the power supply for the ballast transformer 14 and vapor lamps L. However, it should be understood that the standby circuit 30 could be electrically connected through the conductors 31 and 32 to some other suitable power supply, such as an alternate A.C. or DC. power supply, if desired.

A current limiting resistor 33 and a charge storage capacitor 34 are electrically connected between terminals 31a and 32a. The capacitor 34 accumulates an electrical charge from the current flowing through the resistor 33 to control a trigger circuit T, as will be more evident hereinbelow.

An alternating current semiconductor 36, known in the art as a Triac, of the trigger circuit T and the standby lamp S are electrically connected between the terminals 31a and 32a.

As is known in the art, and as has been long used for speed control purposes for fractional horsepower A.C. motors, the Triac 36 permits electrical current to flow between terminals 36a and 36b thereof in response to presence of an input signal at a trigger terminal 360. A resistor 36d electrically connects the trigger terminal 360 to the terminal 32a.

A bidirectional alternating current semiconductor switch 38, known in the art as a Diac, is electrically connected between the trigger terminal 360 of the Triac 3 5 and a common terminal 33a between the resistor 33 and the charge storage capacitor 34. The Diac 38 senses the voltage represented by the charge accumulated on the charge storage capacitor 34 and provides a trigger signal to the trigger terminal 360 of the Triac 36, causing the Triac 36 to permit current to flow between the terminals 36a and 36b thereof. The resistor 36d dissipates the current from the trigger signal passing from the charge storage capacitor 34 through the Diac 38 and protects the Diac from excessive signal levels.

A control switch 40, which is a contact responsive to the control relay 22 in the sensing circuit 20, and a current limiting resistor 41 connected in series with the switch 40 are electrically connected in parallel with the charge storage capacitor 34 between a terminal 38a of the Diac 38 and the terminal 32a. The switch 40 is norting current to flow through the resistor 41 between the terminals 33a and 32a when the relay 22 receives current. Closing of the contact 40 and flow of current through the resistor 41 bypasses the charge storage capacitor 34 and prevents electrical charge from accumulating in the charge storage capacitor 34. As will be more evident hereinbelow, bypassing'of the charge storage capacitor 34 prevents the Diac 38 from receiving a control signal and accordingly prevents the trigger circuit T from energizing the standby lamp S.

A plurality of voltage waveform diagrams are illustrated in the accompanying drawings at FIG.2(A) through FIG.2(F), inclusive. FIG.2(A) illustrates the voltage waveform diagram across one of the vapor lamps L when the lamp L is energized or ignited with the vapor therein relatively cool. When the lamp L is energized with a relatively cool vapor therein, the voltage drop across such lamp is a relatively low level, as is indicated at 51( FIG.2(A)). For example, the voltage drop across a 400 watt mercury vapor lamp is approximately volts. When the vapor lamp L is initially en- 'ergized at such relatively low voltage levels, the illumination output thereof is dim and generally unsatisfactory for illumination purposes.

After ignition of the lamp L, the current passing through the lamp L heats the vapor therein and gradually increases the voltage drop across the lamp L. As the vapor in lamp L warms and the voltage drop across the lamp L increases, the illumination output of the lamp L reaches a desired minimum output level satisfactory for illumination purposes. The voltage level at which the lamp L reaches the desired minimum illumination output level is indicated at 52 in the accompanying drawing (FIG.2(A)). The vapor in the lamp L continues to Warm and the voltage drop thereacross continues to increase until a maximum current established by the ballast transformer 14 and capacitor 15, as has been set forth hereinabove, is reached. The voltage drop at which the maximum current through the lamp L is reached is indicated in the accompanying drawings at 53 and is typically 400 volts peak-to-peak for a single lamp L. If two or more lamps L are connected in series, the peak-to-peak voltage across the series connected lamps increases accordingly.

The voltage waveform appearing at the terminal a is illustrated in the accompanying drawings at FIG. 2(8). The presence of the diode 29 and the sensing circuit 20 of the control circuit K limits the voltage at the terminal 25a during alternate half-cycles of the voltage waveform across the lamps L, as is indicated at 54 in the accompanying drawings. On the other alternate half-cycles of the voltage waveform across the lamps L, the potential at the terminal 25a is generally similar to the voltage waveform appearing across the lamps L.

The voltage waveform across the control relay 22, without the capacitor 23 connected therwith, is generally similar to the voltage waveform at the terminal 25a, with the magnitude thereof reduced due to the presence of the voltage divider network 25 as has been previously setforth. With the capacitor 23 electrically connected with the relay22 in the manner set forth hereinabove, the capacitor 23 removes the high frequency transient effects and provides a relatively smooth gradually increasing voltage (FIG.2(C)). The voltage waveform across the relay 22 with the capacitor 23 connected therewith is indicated at 57 in the accompanying drawings. 7

As has been previously set forth, the magnitude of the resistors 26, 27 and 28 in the voltage divider network 25 is chosen so that the voltage waveform 57 achieves a sufficient magnitude to cause sufficient current flow to energize the control relay 22 at the time that the illumination output of the lamps L is at the desired level, as indicated at 521in. the accompanying drawings (FIG.2(A)) and at 57a in the waveform 57.

As has been set forth hereinabove, when the relay 22 is energized, the contact switch40 closes and bypasses the charge storage capacitor 34, preventing the trigger circuit T from operating and energizing the standby lamp S.

After the vapor lamps L have achieved the desired maximum illumination output level and the desired operating voltage, as indicated at 53 in the accompanying drawings, the lamps L will continue to provide illumination and light energy for the desired intended use.

In the event of a temporary interruption in operating power at the input terminals 1 1a and 12a of the apparatus A, the lamps L become de-energized.

A voltage waveform illustrating the voltage waveform appearing across the lamps L in the event of such de-energization is illustrated generally in the accompanying drawing FIG.2( D). The vertical scale of the voltage waveform in FIG. 2(D) has been reduced by one half from that used in FIG.2(A), FIG.2(B) and FIG.2(C), for reasons to be more evident hereinbelow.

A temporary cessation of power from the power supply to the input terminals 1 1a and 12a of the apparatus A is indicated generally in the accompanying drawings at 58. At such time, the voltage acrossthe lamps L becomes substantially zero volts due to the lack of input voltage at the input terminals 1 la and 12a. As has been set forth hereinabove, the presence of the heated vapor in the vapor lamps L inhibits re-ignition thereof until the vapor cools to a sufiicient degree to permit the voltage present at the terminals 20a and 20b to re-ignite the lamps L. A voltage waveform indicating the voltage waveform appearing across the terminals 20a and 20b when the power supply to the apparatus A is temporarily interrupted and the heated vapor in the lamps L inhibits re-ignition of the lamps L is illustrated generally in the accompanying drawings at 60. The peak voltage of the waveform 60 is generally of twice the magnitude of the desired operating voltage level of the lamps L when such lamps are energized. In order to save space and preserve clarity in the accompanying drawings, the vertical scale of the voltage waveform in FIG.2(D) has been reduced to one-half that of the voltage waveforms appearing in FIG.2(A), FIG.2(B),'and FIG.2(C).

Since the voltage required to re-ignite the lamps L with the heated vapor therein is generally four or five times the magnitude of the desired operating voltage, the voltage waveform 60 is insufficient in magnitude to reignite the lamps L shortly after the power failure indicated at 58.

With the present invention, it has been determined that the inclusion of the clamping diode 29 to coact with the capacitor 15 provides a clamping effect and substantially increases the positive swing of the voltage waveform present at the terminals 20a and 20b of the lamps L. The voltage waveform present at the terminals 20a and 20b is indicated generally in the accompanying drawings at 62. The diode at 29 blocks current flow between the terminals 2% and 20b during alternate halfcycles of the waveform 60, causing the capacitor to charge. During the alternate half-cycles of the waveforms 60, the diode 29 conducts in response to the voltage of the waveform 60. The voltage drop across the diode 29 in addition to the voltage caused by the charge on the capacitor 15 causes the substantially unidirectional waveform 62 to appear at the terminals a and 20]: across the lamps L. Accordingly, the peak voltage of the waveform 62 is substantially twice the peak voltage of the waveform 60, aiding in re-ignition of the lamps L at an earlier time.

Further, with the diode 29 in the sensing circuit 20, the voltage at the terminal a is limited to very small variations from zero volts. The voltage waveform appearing at the terminal 25a when the voltage waveform 62 appears at the terminals 26):: and 2413b of the lamps L is illustrated generally in the accompanying drawings at 64. With the small variations of the voltage waveform 64 about zero volts, the control relay 22 receives insufficient energy to operate.

When the control relay 22 receives insufficient energy, the switch 4d remains open, causing the current from the resistor 33 to flow into the capacitor 34 and charge same. The capacitor 34 continues to charge and increase the voltage at the terminals 331; and 38a until the Diac 38 permits the control pulse to pass therethrough, energizing the trigger contact at 36c of the Triac 36 permitting current to flow from the input terminal 31 through the standby lamp S and the conductive Triac 36 to the terminal 32. In this manner, the standby lamp S is energized by the sensing circuit 20 and the standby circuit of the control circuit K in response to a temporary interruption of power to the vapor lamps L.

After the vapor in the lamps L has cooled to a sufficient degree to permit the lamps L to re-ignite, the voltage waveform across the lamps L is initially a low voltage level, as indicated at 511 in FIG. 2(A). At this time, the voltage waveform 57 has not reached sufficient magnitude to energize the relay 22, and the contact 40 remains open permitting the standby lamp S to remain energized.

As the vapor in the lamp L warms and the voltage drop thereacross increases towards the magnitude 52 when the illumination output of the lamps L is at a desired minimum operating level, the magnitude of the voltage waveform 57 present across the control relay 22 increases until a magnitude indicated at 57a is reached, energizing the control relay 22 and closing the switch 40.. When the switch 4i) closes, the capacitor 34 is bypassed and the current flowing through the resistor 33 flows through the resistor 41, preventing the capacitor 34 from charging.

In this manner, the control circuit K provides standby illumination until the lamps L reach the desired minimum illumination output level necessary for illumination purposes. it should be understood that various resistance values for the resistors 26, 27 and 28 of the voltage divider network 25 can be selected in accordance with the impedance of the control relay 22.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, materials, components, circuit elements, wiring connections and contacts as well as in the details of the illustrated circuitry and construction may be made without departing from the spirit of the invention.

We claim:

1. An apparatus for providing standby illumination when a vapor lamp is de-energized in response to an interruption of electrical power to the vapor lamp. comprising:

a. sensing means connected in parallel with the vapor lamp for sensing the operating condition of the vapor lamp, said sensing means comprising:

1. control means for sensing the de-energization of the vapor lamp;

2. voltage divider means for protecting said control means from high voltage levels present when the vapor lamp is tie-energized; and

3. clamping means for increasing the voltage present across the vapor lamp when the vapor lamp is de-energized to facilitate re-ignition of the vapor lamp; and

b. standby means for furnishing standby illumination when the vapor lamp is de-energized, comprising: 1. standby lamp means;

2. charge storage means for accumulating an electrical charge;

3. trigger means for energizing the standby lamp in response to a predetermined charge present on said charge storage means; and

4. switch means responsive to said control means of said sensing means for preventing charge from accumulating in said charge storage means when the vapor lamp is energized.

2. The structure of claim 1, wherein said control means of said sensing means comprises:

a. a relay receiving current from said voltage divider means when the vapor lamp is energized, said relay receiving insufficient current to operate when the vapor lamp is de-energized.

3. The structure of claim 2, further including: capacitor means connected in parallel with said relay for isolating said relay from short term transient effects.

4. The structure of claim 1, wherein said voltage divider means comprises:

a. a first resistor connected in series with said control means;

b. a second resistor connected in parallel with said series connected first resistor and control means.

5. The structure of claim 4, wherein said voltage divider means comprises:

a voltage drop resistor connected in series with said first resistor and said control means, and further connected in series with said second resistor connected in parallel with said series connected first resistor and control means.

6. The structure of claim 1, wherein said clamp means comprises:

means for unidirectionally biasing the voltage across the vapor lamp when the vapor lamp is deenergized. v

7. The structure of claim 1, wherein said switch means comprises:

relay contact means responsive to said control means for short-circuiting said charge storage means when the vapor lamp is energized.

8.. The structure of claim 1, wherein said voltage divider means comprises:

a. means for establishing a voltage level indicative of a desired illumination output from the vapor lamps; and

b. said control means responding at the established voltage level to control said switch means of said standby means to deactivate said standby lamp.

9. A control circuit for energizing a standby light source to provide standby illuminationwhen a vapor lamp is de-energized in response to an interruption of electrical power to the vapor lamp, comprising:

a. sensing means connected in parallel with the vapor lamp for sensing the operating condition of the vapor lamp, said sensing means comprising:

1. control means for sensing the de-energization of the vapor lamp;

2. voltage divider means for protecting said control means from high voltage levels present when the vapor lamp is de-energized; and

3. clamping means for increasing the voltage present across the vapor lamp when the vapor lamp is de-energized to facilitate re-ignition of the vapor lamp; and

b. standby means for energizing the standby light source when the vapor lamp is de-energized, comprising:

1. charge storage means for accumulating an electrical charge;

2. trigger means for energizing the standby lamp in response to a predetermined charge present on said charge storage means; and

3. switch means responsive to said control means of said sensing means for preventing charge from accumulating in said charge storage means when the vapor lamp is energized. 

1. An apparatus for providing standby illumination when a vapor lamp is de-energized in response to an interruption of electrical power to the vapor lamp, comprising: a. sensing means connected in parallel with the vapor lamp for sensing the operating condition of the vapor lamp, said sensing means comprising:
 1. control means for sensing the de-energization of the vapor lamp;
 2. voltage divider means for protecting said control means from high voltage levels present when the vapor lamp is deenergized; and
 3. clamping means for increasing the voltage present across the vapor lamp when the vapor lamp is de-energized to facilitate re-ignition of the vapor lamp; and b. standby means for furnishing standby illumination when the vapor lamp is de-energized, comprising:
 1. standby lamp means;
 2. charge storage means for accumulating an electrical charge;
 3. trigger means for energizing the standby lamp in response to a predetermined charge present on said charge storage means; and
 4. switch means responsive to said control means of said sensing means for preventing charge from accumulating in said charge storage means when the vapor lamp is energized.
 2. voltage divider means for protecting said control means from high voltage levels present when the vapor lamp is de-energized; and
 2. charge storage means for accumulating an electrical charge;
 2. voltage divider means for protecting said control means from high voltage levels present when the vapor lamp is de-energized; and
 2. trigger means for energizing the standby lamp in response to a predetermined charge present on said charge storage means; and
 2. The structure of claim 1, wherein said control means of said sensing means comprises: a. a relay receiving current from said voltage divider means when the vapor lamp is energized, said relay receiving insufficient current to operate when the vapor lamp is de-energized.
 3. The structure of claim 2, further including: capacitor means connected in parallel with said relay for isolating said relay from short term transient effects.
 3. switch means responsive to said control means of said sensing means for preventing charge from accumulating in said charge storage means when the vapor lamp is energized.
 3. clamping means for increasing the voltage present across the vapor lamp when the vapor lamp is de-energized to facilitate re-ignition of the vapor lamp; and b. standby means for energizing the standby light source when the vapor lamp is de-energized, comprising:
 3. trigger means for energizing the standby lamp in response to a predetermined charge present on said charge storage means; and
 3. clamping means for increasing the voltage present across the vapor lamp when the vapor lamp is de-energized to facilitate re-ignition of the vapor lamp; and b. standby means for furnishing standby illumination when the vapor lamp is de-energized, comprising:
 4. switch means responsive to said control means of said sensing means for preventing charge from accumulating in said charge storage means when the vapor lamp is energized.
 4. The structure of claim 1, wherein said voltage divider means comprises: a. a first resistor connected in series with said control means; b. a second resistor connected in parallel with said series connected first resistor and control means.
 5. The structure of claim 4, wherein said voltage divider means comprises: a voltage drop resistor connected in series with said first resistor and said control means, and further connected in series with said second resistor connected in parallel with said series connected first resistor and control means.
 6. The structure of claim 1, wherein said clamp means comprises: means for unidirectionally biasing the voltage across the vapor lamp when the vapor lamp is de-energized.
 7. The structure of claim 1, wherein said switch means comprises: relay contact means responsive to said control means for short-circuiting said charge storage means when the vapor lamp is energized.
 8. The structure of claim 1, wherein said voltage divider means comprises: a. means for establishing a voltage level indicative of a desired illumination output from the vapor lamps; and b. said control means responding at the established voltage level to control said switch means of said standby means to de-activate said standby lamp.
 9. A control circuit for energizing a standby light source to provide standby illumination when a vapor lamp is de-energized in response to an interruption of electrical power to the vapor lamp, comprising: a. sensing means connected in parallel with the vapor lamp for sensing the operating condition of the vapor lamp, said sensing means comprising: 